Speed Velocity Acceleration

Transcription

1 Speed Velocity Acceleration

2 How fast? If you wanted to calculate Usain Bolt s average speed during a race, what information would you need? 1Kwv0

3 Reference points How do you know the rocket is in motion? In order to tell that something is moving, you have to observe it in relation to a reference point, something that appears to stay in place

4 Reference points can be moving or unmoving Non moving objects, such as building or trees, are useful references point Moving objects can also be used: Ex: if you are in the plane, you could watch the birds fly by and see their position changing relative to your own

5 Speed depends on distance and time Speed depends on the distance traveled and the time it took to get there. Speed = distance (m) / time (s) The standard units for speed are in meters per second (m/s) If a hot air balloon rises 50m in 10s, what is the speed? 50m/10s = 5 m/s

6 Calculate Usain Bolt s speed If Usain Bolt finished the 100m dash in 9.58s in 2009 (setting a world record), how fast was he going? Speed = distance (m) / time (s) = 100m / 9.58s = 10.4m/s In miles per hour? 23 mph!!! (1609 meters in a mile, 3600 seconds in an hour)

7 Determining average speed Could Usain Bolt maintain a speed of 23 mph for an entire hour? No. Most of the time objects do not travel at a constant speed. Therefore, it is useful to calculate average speed: Average speed = total distance(m) / total time(s)

8 Calculate the average speed Suppose someone is driving from one city to the next and it takes them 3 hours. Their speed changes because of weather, traffic, etc. What is their average speed? Distance traveled (km) Hour Add up the total distance 2. Divide by the total time = = 328, 328/3 = 109 km/h

9 More practice If the average speed of a car is 110 km/h, how long will it take the car to travel 715 km? Speed = distance / time 110 km/h = 715 km / (x) 110 (x) = 715 x = 6.5 hours

10 1. Calculate the speed of something in the classroom! On a sheet of paper, answer these questions in complete sentences, and then find an object to measure: 1. Describe the object you are measuring the speed of 2. What supplies will you need to help you measure the speed accurately? 3. Take data and write an equation to calculate the speed of the object Once you have completed this for one object, repeat for a second object. *Turn in when finished

11 2. Ramp height and marble speed Copy this data table and question into your science notebook. How does the angle (height) of a ramp affect the time it takes a marble to travel 30cm? Ramp height T1 (cm) 4 cm (just clipboard) 6 cm 8 cm T2 T3 Avg Time

12 Questions Collect data, write and answer questions #1-5 in your notebook. Show your work! 1. Write two observations and two problems Calculate the average speed in cm/s (centimeters per second) 2. The average speed at 4cm is: 3. The average speed at 6cm is: 4. The average speed at 8cm is: 5. How does the angle of the ramp affect speed?

13 Story problem time! 1. Write your first and last name at the top of the index card 2. Write a title for your problem 3. Write a story problem about speed, time, and distance. Make sure all information to solve the problem is included! 4. Trade cards with someone else, and solve the problem written by your partner. Write the full equation and show your work in your science notebook.

14 Velocity Two birds leave the same tree at the same time. They both fly at 10 km/h for 1 hour, 15 km/h for 30 minutes, and 5 km/h for 1 hour. Why don t they end up at the same destination? They went in different directions! Direction matters.

15 Velocity The speed of an object in a particular direction is the object s velocity. Speed and velocity do not mean the same thing!! These cars might have the same speed, but do they have the same velocity?

16 Examples of velocity Which statement represents velocity: A. 25 m/s forward B. 1,500 km/hour C. 55 m/h south D. 10 m/s Answer: A and C show velocity. They show speed and direction

17 Changing velocity Velocity changes as speed OR direction changes! Example: A bus traveling 15 m/s south turns to travel east Write down an example of change in velocity. Share your example with your table.

18 Acceleration Which scenarios are examples of acceleration? A. B. C. D. A plane taking off A car stopping at a stop sign Jogging on a winding trail Driving around a corner Answer: They are all examples of acceleration! Acceleration is how fast velocity changes. If speed or direction changes, acceleration has happened

19 Calculating acceleration Acceleration is the rate of change in velocity, so: Acceleration = Final velocity - Starting velocity (m/s) Time it takes to change velocity (s) Units: -Velocity is in m/s -Time is in seconds -Acceleration is in meters per second per second m/s/s

20 Practice Using the equation, solve the following problem: Acceleration = (Final velocity - Initial velocity) / Time A plane passes over Point A with a velocity of 8,000 m/s north. Forty seconds later it passes over Point B at a velocity of 10,000 m/s north. What is the plane s acceleration from A to B? Acceleration = 10,000 m/s - 8,000 m/s / 40 s = 2,000 m/s / 40 s = 50 m/s/s north

21 More practice At point A, a runner is jogging at 3 m/s. Fifty seconds later, on a hill at Point B, the jogger s velocity is only 1 m/s. What is the jogger s acceleration from Point A to Point B? Acceleration = Final V - Initial V / time Acceleration can be = 1 m/s - 3 m/s / 50s positive (velocity increased) or = - 2/50 negative (velocity = m/s/s up decreased)!!!

22 Are we accelerating RIGHT NOW? An object traveling in a circular motion is always changing its direction, therefore velocity is always changing, so acceleration is occurring

23 Story problem time! 1. Write your first and last name at the top of the index card 2. Write a title for your problem 3. Write a story problem about velocity and acceleration. Make sure all information to solve the problem is included! 4. Trade cards with someone else, and solve the problem written by your partner. Write the full equation and show your work in your science notebook.